Chemical self-diffusion coefficients, D, as a function of temperature and metal vapor pressure, PCd, were studied in undoped single crystals at high temperatures. The value of D was about 3 orders of magnitude faster than that for self-diffusion under the same conditions. It was shown that doubly-ionized interstitial metal atoms were the predominant diffusible defects at high metal vapor pressures. The value of D was found to be almost independent of the metal vapor pressure for undoped CdSe at high PCd. At 565 to 700C, D could be described by: